1. Field of the Invention
The present invention relates to lower limb prostheses in general, and, in particular, to a shock module prosthesis having a spring and/or fluid resilient element for smooth impact absorption during use of the prosthesis, and also having an adjustable torque-resisting cuff permitting rotational compliance of the lower leg and foot.
2. Description of the Related Art
Various types of lower limb prostheses are known in the prior art. Such devices generally include some form of attachment for coupling the device to the dorsal end of the limb and a leg and/or foot member extending to the ground to support an amputee's weight. These devices generally attempt to simulate the structure and/or the performance of the human leg and foot.
Among the features desirable in a lower limb prosthesis is the incorporation of some means for providing impact absorption and/or dampening during use of the prosthesis, without sacrificing the ability to reliably and predictably support the amputee's body weight. Such impact absorption permits the amputee to participate in activities with comfort and minimal stump trauma, hence allowing the amputee to be mobile for longer periods of time. Also desirable is a convenient means to selectively adjust the degree of impact absorption to suit the particular attributes (e.g., weight) and activity (e.g., walking, running, jumping, etc.) of the amputee.
Impact absorption or, alternatively, shock absorption is normally achieved by the utilization of some form of resilient means, such as a spring, a member fabricated from a resilient material, or a compressible fluid. It should be understood that impact absorption in a prosthesis is simultaneously accompanied by energy absorption/storage and eventually energy release. Such energy release during use of the prosthesis usually aids in forward motion by providing lift and thrust forces to the foot region, thereby permitting the amputee to expend less energy.
Impact absorption in lower limb prostheses is typically achieved by utilizing two or more elongated telescoping members with a resilient means disposed therebetween. Axial forces acting on such members cause relative axial or, alternatively, longitudinal motion between them, with the resilient means providing energy storage and release. Furthermore, optimal performance of such prostheses occurs when there is maintained between these members a smooth relative motion. Unfortunately, a limitation of many such devices is that dirt, debris, and other such particles are free to enter the interface between the telescoping members and upset the smoothness of their relative motion. Thus, it is desirable to incorporate a means for restricting such entrance of dirt, debris, and other particles.
Another desirable feature of lower limb prostheses is the incorporation of some means for allowing rotational compliance of the lower leg and foot relative to the stump of the amputee. Such rotation is beneficial and simulates the action of a natural human knee/ankle in a number of activities that involve the twisting of a person's body with respect to their planted foot, such as golf, tennis, and the like. Rotational compliance in lower limb prostheses is typically achieved by utilizing telescoping members as described above, wherein the interface between such members is cylindrical, permitting them to rotate with respect to each other. However, unrestrained compliance is undesirable, as the foot would be free to twist unnaturally. Thus, it is desirable to incorporate a means for providing torsion-resistance against the rotation of the lower leg and foot relative to the stump of the amputee, and for returning the foot to its natural forward orientation after each rotational movement. Also desirable is a means for selectively adjusting the degree of torsion-resistance, to suit the particular attributes and activity level of the amputee.
The prior art describes many energy storing prostheses which utilize resilient means to cushion impact forces and/or to accentuate the amputee's movements. An example is U.S. Pat. No. 4,883,493 to Martel et al. which illustrates a lower limb prosthesis comprising a pre-loaded heavy duty coil spring and a damper piston mounted between telescoping shafts, using air as a compressible damping fluid. Although this prosthesis provides impact absorption, it encompasses several limitations. One limitation is that the pre-loaded spring provides for a jarring effect at foot/ground contact and a hard stop at spring extension. Such impact shocks may be tolerable to an athlete during running but are unreasonably uncomfortable for an ambulatory amputee. Another limitation is that the bolt-slot assembly restricts any rotational motion of the lower leg and foot. Another limitation is that the prosthesis utilizes the bolt-slot assembly to maintain the vertical position of the damper piston as the stump-supporting shaft vertically oscillates. As a result, the bolt experiences high shear stress caused by the pressure exerted against the damper piston by the compressed air during energy release and thrust. Moreover, the bolt is also vulnerable to shear stress associated with the twisting of the amputee's body with respect to their planted foot, as described above. These undesirable stresses adversely influence the performance of the prosthesis and necessitate frequent maintenance thereof. Yet another limitation is that there is no means for keeping atmospheric debris from entering the interface between the shafts, necessitating frequent disassembling and cleaning.
An example of a prosthesis which provides impact absorption, rotational compliance, and torsion-resistance is set forth in U.S. Pat. No. 5,458,656 to Phillips. In the preferred embodiment of this invention two telescoping cylindrical pylon members are connected by one or more elongated leaf spring elements. Normal and torsional forces imposed on the pylon members cause relative motion therebetween. A corresponding storage/release of energy in the leaf spring element(s) concurrently provides both impact absorption and torsion-resistance. The storage of energy associated with impact absorption is provided by an outward flexure of the leaf spring element(s). In contrast, the storage of energy associated with torsion-resistance is provided by a twisting of the leaf spring element(s).
Although the prosthesis of Phillips '656 utilizes a highly adaptable and effective design, it is very expensive to manufacture and has several characteristics that limit its clinical efficacy. One characteristic is that in order to vary the degrees of impact absorption and torsion-resistance the amputee must replace the leaf spring element(s), which is somewhat inconvenient. Another characteristic is that axial and torsional forces can cause excessive bending and twisting of the leaf spring element(s) which can create local regions of undesirably high stress. Another characteristic is that the outward flexure of the spring element(s) results in a larger effective width profile for the prosthesis, which can make cosmetic finishing more difficult. Yet another characteristic is that there is no means disclosed for keeping atmospheric debris from entering the interface between the pylon members.
A more recent U.S. Pat. No. 5,702,488 to Wood et al. describes another prosthesis that provides impact absorption, rotational compliance, and torsion-resistance. Impact absorption is provided via compression of a compressible volume of fluid which is enclosed between a piston head and cylindrical piston chamber. Torsion-resistance is provided by four resilient cushions that impede the rotation of a torsion key attached to the piston head.
Unfortunately, there are a variety of limitations associated with the prosthesis illustrated by Wood '488. One limitation is that it has a complex design, including the placement of an O-ring seal, a wear ring, two O-ring bumpers, and a retainer block within the interface between the telescoping piston head and piston chamber. This design translates into a heavier, expensive prosthesis that requires high maintenance and frequent adjustment. Another limitation is that torsion forces applied to the prosthesis result in local regions of undesirably high stress in the torsion key, which necessitates frequent maintenance. Another limitation is that the compressible fluid, by itself, provides less impact absorption than other prostheses. Another limitation is that there is no means for varying the torsion-resistance of the prosthesis, except for replacing the resilient cushions, which is inconvenient and cumbersome. Yet another limitation is that there is no means for keeping atmospheric debris from entering the interface between the piston head and piston chamber.
Of course, other shock absorbing means in prostheses simply induce a cushioning effect by utilizing strategically placed resilient materials, such as, for example, rubber in a prosthetic foot, socket liner, or stump socket. Those of ordinary skill in the art will readily comprehend that such cushioning means are of limited effectiveness and can only serve in a secondary capacity. Also, such shock absorbing means are typically integral with the foot or socket/liner and thus cannot be used with other prosthetic feet in a modular manner.
Thus, although the prior art illustrates many impact absorbing prostheses, none provide the benefits of selectively adjustable impact absorption, rotational compliance, conveniently adjustable torsion-resistance, and a means for preventing debris from entering and upsetting the smoothness of the relative motion of telescoping members, all in a relatively simple but highly effective construction which may be utilized in combination with a broad selection of prosthetic feet and sockets in a modular manner.